The present invention relates to an infrared image pickup device for converting a temperature distribution or profile of an object to a two-dimensional image which is displayed on a screen.
A conventional pyroelectric infrared image tube using a pyroelectric material as a target is proposed to convert a temperature distribution of an object to a two-dimensional image. This pyroelectric infrared image tube has been receiving a great deal of attention recently since it can be used with a standard television system. The operation of this infrared image tube will first be described. Infrared rays emitted from a surface of an object in accordance with a temperature distribution thereof are focused on a target through an optical system. When an image representing an infrared ray intensity distribution is formed on the target, the rays are absorbed in the target made of a pyroelectric material so as to cause a change in the temperature distribution on the surface of the target. This change causes a pyroelectric effect which induces a charge distribution. This charge distribution is then read in accordance with electron beam scanning, thereby obtaining an image signal representing the temperature distribution. Since the pyroelectric effect is defined as a phenomenon wherein charge is induced in accordance with a change in temperature, incident infrared rays must be shielded/passed by a chopper at a speed of several to ten times per second when a still image is photographed.
The basic arrangement of a conventional image pickup device having the above-mentioned pyroelectric infrared image tube is illustrated in FIG. 1. Infrared rays incident on a target 2 in a pyroelectric image tube 1 are shielded/passed by a chopper 4 which is rotated by a motor 3 so as to form a charge distribution image on the target 2. This image on the target 2 is scanned with an electron beam 6 by using a deflection coil 5 and is read from the target 2. The read image signal is amplified by an amplifier 7 and is then subjected to necessary signal processing in a signal processor 8. A resultant image signal is supplied to a display monitor 9 and is displayed thereon. A light-emitting element 10 and a photosensor 11 cooperate to detect a chopping timing of the chopper 4, and the motor 3 is controlled so as to synchronize the chopping timing with a vertical sync pulse of the electron beam. For example, when the chopper 4 is turned on/off for every eight fields, a signal obtained by 1/16 frequency-dividing a vertical sync pulse VD from a television standard sync generator 12 is compared by a phase comparator 13 with a pulse from the photosensor 11. An error signal from the phase comparator 13 is supplied to a motor control circuit 14 to control the speed of the motor 3 such that the chopper 4 is turned on/off for every eight fields. The sync pulse VD from the sync generator 12 is also supplied to a cathode power supply 15, a deflection power supply 16 and the like to control electron beam scanning. The sync pulse VD is also supplied to the signal processor 8 to control signal fetch timing and the like.
In the conventional infrared image pickup device, as shown in FIG. 1, an infrared image signal from an image pickup section 17 is processed by the signal processor 8, and the processed signal is displayed on the display monitor 9. In this sense, the conventional infrared image pickup device processes only the infrared signal. In addition, even when visible image information is added to the infrared information shown in FIG. 1, an infrared image signal from the image pickup section 17 is processed by the signal processor 8 so as to display an infrared image on the display monitor 9, and at the same time, a visible image signal from a visible image pickup section 18 is processed by a signal processor 19 so as to display a visible image on a display monitor 20, as shown in FIG. 2. In this manner, the infrared and visible image pickup units are simply arranged in parallel with each other.
In a method of displaying only the infrared image signal in FIG. 1, since the shape of the infrared image generally differs from that of the visible image, it is very difficult for an observer to decide which part of the object is photographed, resulting in inconvenience.
In a method shown in FIG. 2, assume that the infrared and visible image pickup sections 17 and 18 are used independently of the display monitors 9 and 20 so as to measure the temperature distribution of the object, that resultant images are recorded in VTRs, and that the images are reproduced and supplied to the signal processors 8 and 19. In this case, it is apparent from the above description that two VTRs for infrared and visible images are required. In addition, counts of the counters of these VTRs must be stored when the infrared and visible images at given time are observed, resulting in inconvenience for measuring the temperature distribution of the object. Furthermore, when the observer wishes to observe an infrared image in more detail (e.g., when the observer continues to observe an infrared still image on the display monitor 9), VTR signals representing visible images are continuously transmitted, and the infrared image is not synchronized with the visible image.
In order to overcome the above drawback, a method is proposed to superpose an infrared image with visible information. In this case, as shown in FIG. 3, infrared and visible image signals from infrared and visible image pickup sections 17 and 18 are mixed by a mixer 21, and a composite signal is then processed by a signal processor 22. A processed composite signal is displayed on a display monitor 23. In other words, as shown in signals (a) to (c) of FIG. 4, an infrared image output signal (a) from the infrared image pickup section 17 is mixed by the mixer 21 with the visible image output signal (b), and the composite signal (c) is generated by the mixer 21. Reference symbol T.sub.0 denotes a signal transmission time interval for one-field picture. According to this conventional method, assume that only the infrared image pickup section 17 is separated from the system so as to measure the temperature distribution of the object, that a resultant image signal is recorded in a VTR, and that the image signal is reproduced from the VTR so as to observe the temperature distribution of the object. In this case, since only the infrared image is displayed on the display monitor, it is difficult for the observer to decide which portion of the object is displayed. In addition, when an image is obtained by superposing the visible profile image on the infrared image, it is an inconvenience to observe only the infrared image so as to check the temperature profile of the object.